Remote command execution through file upload in contao/core-bundle

Contao is an Open Source CMS. In affected versions a back end user with access to the file manager can upload malicious files and execute them on the server. Users are advised to update to Contao 4.13.49, 5.3.15 or 5.4.3. Users unable to update are advised to configure their web server so it does not execute PHP files and other scripts in the Contao file upload directory.